The present invention relates to a gas turbine by-pass system, and more specifically, to a gas turbine by-pass system and method for operating the gas turbine by-pass system that provides a safe and secure environment for workers to avoid contact with extremely hot gases.
Conventional gas turbine engines burn natural gas, with the hot gasses from the combustion of the natural gas driving a turbine. The heated gases (typically about 1000 degrees Fahrenheit) exiting the turbine pass through an exhaust duct to a heat recovery steam generator (HRSG). The heat from the gasses is then recovered in the HRSG to produce steam, which in turn is used to drive a steam turbine. The cooled gases exit the HRSG to be exhausted through a short stack.
Conventional gas turbines are equipped with a set of dampers or diverters that allow the turbine to operate in either a simple-cycle or a combined-cycle mode. The bypass damper controls flow through the bypass or simple-cycle stack, and the isolation damper controls flow through the HRSG. During start-up operations, the isolation damper is closed, thereby preventing flue gas flow through the HRSG, and the bypass damper is open, allowing flue gas to exit through the bypass stack. This is referred to as simple-cycle operation. Once the turbine has completed start-up procedures the isolation damper is opened and the bypass damper is closed, consequently redirecting flue gas flow through the HRSG. The hot flue gas heats boiler feed water to produce steam, which, once it has reached sufficient quality, is used to drive a steam turbine to produce more electricity. This is referred to as combined-cycle operation.
Gas flow diverters are often employed to deliver hot exhaust gases from a turbine either to a HRSG or to the stack. Many problems are attendant their use due to the large volumes of gases at high temperatures and under substantial pressure that are exhausted by turbines and the necessity that the hinged gas diverter blade be swung into and out of its operative positions relative to the stack and to the steam generator without vibrating and without causing thermal shock on the system. Such diverters are large as are the conduits leading therefrom to the steam generator or to the stack. Consequently, as the conduit to the steam generator must be capable of being safely entered by service personnel, leakage into the HRSG must be prevented when gas flows are diverted to the stack in order to avoid the necessity of placing the turbine out of service.
The diverter dampers that are currently used in gas turbine systems operate to divert the hot exhaust from the gas turbine into the HRSG when the power plant is operated as a combined-cycle facility or into the exhaust stack in the case of simple-cycle operation. Such diverter dampers are typically quite expensive and do not provide long term reliability. Because any maintenance or modification work that may be performed within the HRSG requires that the HRSG be xe2x80x9chuman-safe,xe2x80x9d any leakage from a diverter damper cannot be tolerated. As a result, some manufacturers include an isolation guillotine damper as the back the diverter damper. In using a guillotine damper, the guillotine blade is exposed to very high temperatures on one side and much cooler air on the opposing side, which can lead to warping of the blade. When warping of the guillotine blade occurs, leaks may be created in the diverter damper that allow hot and toxic gasses pass through to the HRSG and consequently endanger the health of the worker in the HRSG.
What is desired, then, and not found in the prior art, is a gas turbine by-pass system that effectively and securely diverts extremely hot gasses from the HRSG in simple mode to provide workers with the safe environment needed to perform their function within the HRSG, and that can further be operated in an inexpensive manner.
It is an object of the present invention to provide a gas turbine by-pass system for use in a gas turbine engine.
It is a further object of the present invention to provide a gas turbine by-pass system having a diverter box that effectively diverts heated gasses from a heat recovering steam generator to allow a worker to service the heat recovering steam generator.
It is yet a further object of the present invention to provide a gas turbine by-pass system having an expansion joint with a truss assembly and a blank off plate that may be moved with a minimal number of workers.
It is another object of the present invention to provide a less expensive gas turbine by-pass system that is reliable and human-safe alternative using a unique monorail/hoist arrangement to handle an expansion joint and a blank off plate without damage and easily replacing flange seals.
The present invention of a gas turbine by-pass system is used between the gas turbine generator outlet nozzle and the inlet of a heat recovery steam generator (HRSG). The gas turbine by-pass system is used to enable a power generation company to switch from producing power in a simple cycle mode (gas turbine generation only) to a combined cycle mode (gas turbine generation and power produced through the HRSG). The gas turbine by-pass system therefore allows the operators to change from combined cycle mode to simple cycle mode to allow maintenance to be performed to the HRSG by crew of human workers.
One embodiment of the gas turbine by-pass system substantially eliminates the need to remove beams and bracing from the stack/silencer support structure. Because weather conditions, such as wind, and other seismic events cannot be predicted, it is crucial that the structure stay intact while the procedure is being effected. The outboard monorail at the outlet end of the diverter xe2x80x9cboxxe2x80x9d and switching track of the monorail make this possible. The entire procedure entails a unique use of monorails, hoists, and the monorail switch track.
Another embodiment of the present design requires removal of some beams and bracing from the support tower in order to remove or replace the blanking plate and the expansion joint. This system may be acceptable for use in areas where the design is governed by wind speed, as it is presumed advance notice of impending wind disturbances (such as hurricanes, tornadoes, thunderstorms, etc.) can be reasonably predicted and the timing of the change-out procedure take place only during xe2x80x9csafexe2x80x9d conditions. However, in those geographic areas where seismic activity governs the structural design of the by-pass system, removing beams and bracing could bring a potentially catastrophic situation to bear, since it is almost impossible to predict the timing of seismic activity.